A. Field of the Invention
The present invention relates generally to oil field tubular members, and more particularly to an encapsulated depleted uranium weighted sinker bar or drill collar and a method of making same.
B. Description of the Prior Art
Many operations associated with drilling and completing oil and gas wells include the use of weighted tubular members. In drilling, the drill pipe is kept in tension and the weight on bit is provided by thick walled heavy sections of pipe known as drill collars immediately above the bit. In wire line operations, the line and associated tools must be pulled into the hole by weights, which are known as sinker bars.
It is desirable that both sinker bars and drill collars have as great a weight per unit length as possible. During drilling, drill collars are under compression and the longer the string of drill collars, the more subject such string is to deflection. By increasing the weight per unit of length, the string of drill collars can be made shorter and effectively more rigid. Also, a shorter string of drill collars requires fewer connections. By reducing the number of connections, the costs associated with reconditioning the drill collars is reduced.
One attempt to provide a drill collar with increased weight per unit length is disclosed in U.S. Pat. No. 3,167,137. The drill collar of the '137 patent includes inner and outer pipes with tool joints connected to either end to form an annular chamber. The annular chamber is filled with lead or an alloy of lead. Since lead is approximately 40% more dense than steel, the drill collar of the '137 patent has a higher weight per unit length than a steel drill collar of substantially the same diameter.
In U.S. Pat. Nos. 2,814,462, and 3,179,188, there are disclosed fluid packed drill collars. The drill collars of the '462 and '188 patents include generally cylindrical inner and outer pipes with tool joints connected thereto to form an annular chamber which contains a fluid and solid bodies movable with respect to the fluid. In certain embodiments disclosed in the '462 and '188 patents, the fluid is disclosed as being mercury. Since the density of mercury is approximately 68% greater than that of steel, a mercury packed drill collar, as disclosed in the '462 or '188 patents, has a higher weight per unit length than a steel drill collar of the same diameter.
It is important to minimize the length of the sinker bar string used in weighting wire line equipment. There are three types of sinker bars; strap-on; solid; and, contact bars. The strap-on type is flexible and is strapped onto the lowering cable, but is not readily used because it typically is of low mass. Solid bars are mounted on the bottom of the wire line tool string and are typically the heaviest sinker bars. However, the presence of the solid bar at the bottom of the tool string makes it impossible to log to the bottom of the hole. When solid bars are used, it is necessary to drill below the lowest area of interest. Contact bars are mounted on the top of the tool string and have means for establishing electrical contact between the wire line and the logging tool.
Wire line logging equipment are run into pressurized wells through lubricators. A lubricator is essentially a pipe having a stuffing box at the top and a valved connection to the well-head at the bottom. The wire line tools and sinker bars are connected together and loaded into the lubricator. The lubricator valve is then opened and then the tools and sinker bars are run into the wellbore. By increasing the weight per unit length of the sinker bars, the length of the sinker bar string can be reduced, thereby reducing the necessary length of lubricator. Also, as with the case of drill collars, fewer connections are necessary to connect together the sinker bar string, thereby reducing the number of places for equipment to malfunction.
It is therefore an object of the present invention to provide an improved oil field weighted tubular member having a higher weight per unit length than heretofore existing members. It is a further object of the present invention to provide a depleted uranium weighted oil field tubular member that is encapsulated, thereby to prevent hazards due to the pyrophoretic properties of uranium metal. It is yet a further object of the present invention to provide an encapsulated depleted uranium tubular member that will withstand abuse and wellbore pressures without deformation.